The present invention relates to a blood vessel dilatation apparatus for restoring the blood stream at a peripheral side of a stenotic portion by dilating it in treating stenosis of a blood vessel. In other words, the present invention relates to a blood dilatation catheter.
It has become possible that an apparatus of Percutaneous Transluminal Coronary Angioplasty (hereinafter referred to as PTCA dilatation catheter) that is used to treat myocardial infarction or angina pectoris into a fine blood vessel or a:complicated lesion portion. This is because a PTCA dilatation catheter having a small diameter and flexible has been developed. The PTCA dilatation catheter has a lumen through which a guide wire is passed. In inserting PTCA dilatation catheter into a blood vessel, it is operated together with the guide wire.
A catheter tube constituting the PTCA dilatation catheter requires at least two lumens: One is used to insert the guide wire therethrough, and the other is used as a path through which an operating fluid for dilating and contracting a dilatation member (balloon) for dilating a stenotic portion of a blood vessel. Thus, heretofore, an uncoaxial porous plastic tube having two uncoaxial lumens or a plastic catheter tube having coaxial inner and outer tubes is used.
The PTCA dilatation catheter having the above-described uncoaxial catheter tube has a characteristic that it can be smoothly pressed into a blood vessel. But the operability of the guide wire is poor. Further, it is not suitable for reducing the diameter of the catheter tube. Therefore, in recent years, the above-described plastic tube having coaxial inner and outer tubes is mainly used.
In dilating the a stenotic portion of a blood vessel, the guide wire is inserted into the stenotic portion and then the dilatation member located at the front end of the blood vessel dilatation catheter is inserted into the stenotic portion. Accordingly, it is preferable that the front side of the blood vessel dilatation catheter is flexible to follow the movement of the guide wire. It is also preferable that the blood vessel dilatation catheter is small (low profile) to allow the dilatation member to arrive at the stenotic portion situated at a peripheral blood vessel. It is also preferable that the rear portion of the blood vessel dilatation catheter located outside proximally from the stenotic portion-present peripheral blood vessel is thicker than the front portion of the blood vessel dilatation catheter to allow the catheter to be smoothly pressed in the blood vessel and secure torque transmittable performance.
To this end, in the above-described plastic tube having the coaxial inner and outer tubes, the diameter of the outer tube is decreased in one stage or a multistage toward the front end of the catheter at a portion a predetermined length rearward from the front end of the catheter. In this construction, the inner diameter of the front end portion of the outer tube is necessarily small. It is preferable that the inner diameter of the rear portion of the outer tube is larger than that of the front end portion thereof to allow smooth flow of the operating fluid for dilating and contracting the dilatation member.
However, in the above-described construction, the inner diameter of the outer tube is large in the rear portion of the catheter. Thus, the clearance between the inner surface of the outer tube and the inner tube is necessarily large. Consequently, at a position corresponding to the rear end portion of the catheter (outer tube), the inner tube may be bent, curved or twisted inside the outer tube when the catheter passes a curved portion of the blood vessel. As a result, the operating fluid for dilating and contracting the dilatation member is prevented from smoothly flowing between the inner tube and the outer tube, which means that it takes long to dilate and contract the dilatation member. Further, a pressing force generated at the rear portion of the catheter is absorbed by intermediate parts thereof and thus cannot be reliably transmitted to the front end thereof.
Therefore, it is an object of the present invention to provide a blood vessel dilatation apparatus which can arrive preferably at a stenotic portion located in a peripheral blood vessel; which can be pressed favorably in the blood vessel (travel performance in blood vessel); which does not intercept a duct of a dilatation member or prevents a liquid from flowing into the dilatation member; and which allows the dilatation member to dilate and contract for a short period of time (preferable in response performance in dilatation and contraction).
It is another object of the present invention to provide a blood vessel dilatation apparatus, of a coaxial construction, which has an inner tube and an outer tube having a small inner diameter at its front portion and a comparatively large inner diameter at its rear portion and which prevents the inner tube disposed inside the outer tube from being bent, curved or twisted.
The object of this invention is to provide a blood vessel dilatation apparatus comprising: an inner tube having a first lumen whose a distal end is open; an outer tube coaxial with said inner tube, having a front end at a position rearward in a predetermined length from said front end of said inner tube, and forming a second lumen between said outer tube and an outer surface of said inner tube; a dilatation member contractible or foldable, having a front end portion secured to said inner tube and a rear end portion secured to said outer tube and communicating with said second lumen in the vicinity of a rear end thereof; a first opening provided at a rear end portion of said inner tube and communicating with said first lumen; and a second opening provided at a rear end portion of said outer tube and communicating with said second lumen, wherein said outer tube has a front part having a comparatively small diameter and located rearward in a predetermined length from a position at which said outer tube and said dilatation member are connected with each other; and a rear part having an inner diameter greater than that of said front part at least in a greater part thereof; and said outer tube is fixed to said inner tube through an inner surface of said rear part.